The invention relates to a lamp, in particular a metal halide discharge lamp, having a protective shield around the light source, wherein the shield is supported by a metal frame mounted to the stem, and a glass envelope fixed to the stem surrounds the shield.
Metal halide lamps typically incorporate a tubular shield surrounding the pressurized arc tube to absorb the impact of dispersing shards in the event the arc tube fractures. This shield is supported by a metal frame mounted to the stem in the lamp. For low to medium wattage lamps the frame is typically in two parts embedded in the stem, and these parts also serve to provide current for the electrodes of the arc tube. See, for example, U.S. Pat. No. 5,532,543.
Since current-carrying members in proximity to the arc tube can cause sodium loss, it is preferable to electrically distance the current carriers from the lateral walls of the arc tube. Note the insulating sleeve on the frame member in U.S. Pat. No. 5,532,543. See also U.S. Pat. No. 5,339,001. While this patent does not show a protective shield, it does show a frame member which supplies only the lower electrode of the arc tube, and a "flying lead" well spaced from the arc tube to supply the upper electrode.
Safety considerations in high wattage metal halide lamps dictate that a protective sleeve be used. However in order to adequately support such a protective sleeve and at the same time prevent sodium loss, it is desirable for the supporting frame to be electrically isolated from the current carriers for the arc tube. Mounting techniques used by OSI and GE for their high wattage protected metal halide lamps incorporate a U-shaped wire frame having metal bands welded to the ends thereof, the bands being welded in place around the glass stem. This allows the frame to be electrically isolated (floating), which is especially desirable for high wattage protected lamps. However the multiple welding steps add to the cost of manufacture, and would preferably be eliminated.